1. Field of the Invention
The invention relates to a method and apparatus for waste water treatment. In particular, the invention relates to the treatment of radioactive hazardous toxic waste materials and the safe disposal thereof.
2. Description of the Art
Contaminated radioactive waste solutions containing high concentrations of chelating agents such as EDTA are sometimes generated during the application of chemical cleaning processes to nuclear equipment such as the secondary side of a nuclear steam generator. There are a variety of disposal techniques for handling these waste solutions.
One method of disposal includes the separation of the hazardous constituents from the non-hazardous constituents and evaporation of the waste water to retrieve solids, which can then be buried in a disposal site. However, current waste disposal regulations make this method unacceptable mainly because the solid hazardous waste contains EDTA, NTA, citric acid or other chelating agents. Chelating agents may leak from the disposal site, migrate through the soil and mix with the ground water supplies, while carrying chemically bonded radioactive or other hazardous species. For this reason, hazardous waste disposal sites set stringent limits on the amount of chelating agent allowed to be present in waste material accepted for burial. In other words, significant concentrations of chelating agent may not be disposed concurrently with radioactive waste.
Another method of disposal involves chelant destruction in which the chelating agent is oxidized or pyrolized into relatively harmless constituents and the radioactive species are disposed of at the burial site. The choice of which method to use is determined by the effectiveness, the cost, and the time required to effect the solution. Volume reduction of the untreated material, for example, by evaporation techniques is effective. However, the costs including capital and operating costs as well as waste site charges makes this volume reduction method unattractive. Further, the final concentration of the chelant may exceed the disposal site limits making the method effectively unavailable. The complexity of various related volume reduction techniques also bears negatively on this technique.
In separation technology the metal ions (predominantly iron and copper) and radionuclides which typically follow them, are separated from the chelant. The former require radioactive disposal and the latter is treated as a non-radioactive hazardous waste. Ion exchange, membrane and magnetic filtration technologies may possibly achieve the desired results for dilute concentrations. These technologies, however, have not been proven in terms of feasibility and cost effectiveness.
With chelant destruction technology, the chelant is transformed into a non-hazardous species. Subsequent processing is then used to reduce the volume of the radioactive waste. Pyrolitic decomposition may be effective but as yet is not licensed. Electrolytic chelant decomposition is relatively slow. Various oxidation techniques appear to be useful but each has its drawbacks. Ozone treatment of the chelant requires expensive equipment and is slow but does not significantly increase waste volume. Also it has not proved to be effective. Peroxide treatment is more cost effective but adds waste volume.